An image capturing apparatus which performs pupil-division-based focus detection using a two-dimensional sensor having micro-lenses on part of the pixels of a solid-state image sensor is conventionally known as a method for detecting an imaging lens' focus state. In this image capturing apparatus, among a large number of pixels constituting the solid-state image sensor, part of the pixels serve as focus-state detection pixels of the imaging lens. With the use of the focus-state detection pixels, which receive light that has passed through part of the pupil area of the imaging lens, and which receive light that has passed through different pupil areas as a pair, the focus-state detection pixels detect the imaging lens' focus state by a phase difference of image signals which are generated by the plural pairs of pixels. This configuration is disclosed in, for example, Japanese Patent Laid-Open No. 2009-003122.
However, in the technique suggested by Japanese Patent Laid-Open No. 2009-003122, since part of the image forming pixels are used as focus detection pixels, a received light amount is small compared to regular pixels. For this reason, there are problems in that the image capturing apparatus is largely influenced by noise and tends to have poor precision in focus detection.